Tech Tent: Do Covid apps work?
Susan Landau, professor of cyber-security at America's Tufts University, examines the various methods in her book People Count: Contact-Tracing Apps and Public Health. She tells Tech Tent how each has fared.
"South Korea has done quite well in controlling the disease. But one has to say that there are cultural aspects to this - as well as the technology, the willingness to wear masks."
That, she explains, would not work in the United States.
Singapore's centralised app has worked well, she says, because citizens have been required to use it in offices, shopping centres and schools. But they have also been forced to hand over lots of very sensitive data.
"It has been used for criminal investigations," she says. "If you're a journalist and people know proximity information, then they know who you've been talking to. And that, of course, can be really dangerous for human rights workers."
As for the decentralised apps, their effectiveness "has become more clear with time". Prof Landau points to a study in the journal Nature which showed that the NHS Covid-19 app had averted hundreds of thousands of cases of the virus.